Cl-CHANNELS play important roles in the regulation of cellular excitability, acidification or of intracellular organelles, cell volume, proliferation, differentiation, and apoptosis in many tissues. But the exact functional role of Cl-channels in human cardiovascular physiology and pathophysiology is still not known. Although mutations in several Cl- channels have been found to result in human inherited diseases, one of these channels has yet to be directly linked to any human cardiac pathology. With our recent success in molecular biological and genetic approaches to effectively address these unanswered questions. The COBRE facilities provide not only genetically engineered (including knock-out, cardiac-specific gene targeting, and conditional expression of a transgene in the heart) mice developed in transgenic core (Core A) but also antisense oligonucleotide techniques and other molecular biological approaches developed in molecular/genomic core (Core B). We are now in a unique position to study the specific role of each individual Cl- channel, which has been impossible in the past due to concomitant expression of multiple types of Cl-channels in the same cardiac cell and the lack of specific pharmacological and molecular tools. The aim of this project is to use both in vivo and ex vivo animal models to delineate the role of Cl-channels in cardiac disease and ischemic preconditioning at whole animal, isolated organ, and single cell levels. Microsurgical techniques that produce pathophysiological stress (such as myocardial ischemia reperfusion) mimic human disease will be superimposed on the genetically engineered animals to determine the cardiac pathophysiological consequences of these gene manipulations. We will test the following hypotheses: 1) cardiac Cl- channel function contributes to the normal cardiac electrophysiological and hemodynamic properties. 2) Cl-channels contribute to ischemia/reperfusion, congestive heart failure, and hypertrophic cardiomyopathy induced cardiac arrhythmias and function changes. 3) CFTR and CL-3 are important mediators in cardiac ischemic preconditioning that may be linked to PKC. This will provide not only new insights into the regulation and physiological and pathophysiological role of Cl-channels but also a better understanding of the physiological and pathological regulation of cardiac function. The functional studies proposed in this project represent a new start to our long-term goal of accurately identify the role of Cl-channels in cardiovascular function.